Wells are commonly drilled to recover hydrocarbons, such as oil and gas, from subterranean formations. Drilling a well typically entails rotating a drill bit positioned at the end of a drill string comprising a plurality of drill pipe segments connected end to end. As the wellbore is drilled, additional segments of drill pipe are added from the surface to reach the desired drilling depth. A wide variety of drill bits are known in the art, each having different attributes that can be considered in selecting a bit for a particular application.
One general type of drill bit is a rotary cone or roller cone drill bit. A rotary cone drill bit generally includes at least one support arm, and most often three support arms. Each support arm has a respective rotary cutter assembly rotatably mounted on a journal. Each rotary cutter assembly typically includes a cavity with a configuration and interior dimensions sized to receive exterior portions of the associated journal therein. Any of a wide variety of bearings, bearing assemblies or other supporting structures may be disposed between interior portions of each rotary cutter assembly and exterior portions of the associated journal, including journal bearings. Surface coatings, such as silver, may be engineered onto bearing surfaces to protect the surfaces. In addition, grease may be used to fill the cavities within the rotary cutter assemblies to provide the lubrication required between the moving parts. Fluid barriers, such as seals and diaphragms may be used to prevent drilling mud from entering into the rotary cutter assemblies. Such fluid barriers may be formed from an elastomer such as hydrogenated nitrile rubber (HNBR).
During drilling with a rotary cone bit, the cutting surfaces of the rotary cutter assemblies are pushed against the bottom of the borehole while rotating the drill bit, which causes the rotary cutter assemblies to rotate about their respective journals. Components within the drill bit, such as the journal bearing, are subjected to severe operating conditions including high unit loading, repetitive shock loading and high contract pressures, which can lead to galling or other degradation of the bearing surfaces.